1. Field of the Invention
The present invention relates to an optical pickup and an optical disc apparatus, which use light beams having different wavelengths to record and/or reproduce information on/from a plurality of types of information recording mediums such as optical discs.
2. Description of the Related Art
As a next-generation optical disc format, a format using a blue-violet semiconductor laser which emits a light beam having a wavelength of about 400 nm to 410 nm as a light source is currently employed.
For providing an optical pickup compatible with the next-generation optical discs, an optical pickup having compatibility with optical discs in different format such as existing CD (Compact Disc) and DVD (Digital Versatile Disc) is desired. As described above, an optical pickup and an optical disc apparatus, which have compatibility with optical discs in formats using different disc structures and different laser specifications in accordance with the different disc structures, are required.
As an optical pickup for recording and reproducing an information signal on/from a plurality of types of optical discs using different wavelengths as described above, there exists an optical pickup including a plurality of objective lenses compatible with the respective optical discs.
The optical pickup using a plurality of objective lenses includes a correspondingly large number of components. Therefore, there is a possibility that the size of the optical disc apparatus or the fabrication cost may be increased.
As an optical pickup for recording and reproducing an information signal on/from a plurality of types of optical discs using different wavelengths, an optical pickup including a single objective lens and an optical element for converting a divergent angle of a light beam incident on the objective lens in accordance with its wavelength is conceivable.
Specifically, Japanese Patent Application Publication (KOKAI) 2005-38575 discloses an optical pickup 100 as shown in FIG. 8. The optical pickup 100 uses an objective lens 103 for focusing a light beam having a first wavelength of about 405 nm on a signal recording face of a first optical disc compatible with the first wavelength. The optical pickup 100 includes a first diffractive element using the objective lens 103 to change an incident angle of a light beam having a second wavelength of about 660 nm so that the light beam is focused on a signal recording face of a second optical disc compatible with the second wavelength and a second diffractive element 104 using the objective lens 103 to change an incident angle of a light beam having a third wavelength of about 785 nm so that the light beam is focused on a single recording face of a third optical disc compatible with the third wavelength.
As the second diffractive element 104, a diffraction grating having a grating height equal to integral multiples of 405 nm and 660 nm corresponding to the first wavelength and the second wavelength as shown in FIG. 9 is used.